In the field of Medical Imaging, one modality is nuclear medicine (gamma camera) imaging. This uses a detector consisting of a scintillator backed by a plurality of photomultiplier tubes (PMTs) with appropriate electronics. A patient is given a radioisotope either by injection or ingestion and the detector(s), after being placed in close proximity to the patient, can determine where the radioisotope goes or has gone.
When the radioisotope emits a gamma photon in the direction of the detector, it is absorbed by the scintillator. The scintillator emits a flash of light (a scintilla) which is detected by the plurality of PMTs. The PMTs nearest to the flash receive a stronger signal than those further away. By measuring the intensity of the flash at each PMT, then performing a calculation, for example a centroid type calculation, a fairly accurate estimation of where the flash occurred is possible.
The output of the PMTs is an electrical current proportional to the amount of light detected by each PMT. The PMT output current can be converted into a voltage and amplified, then integrated to derive the total energy (light) detected by each PMT.
In nuclear medicine imaging, dynamic time varying data may be acquired during the first transit of the bolus of the injected radiotracer. This data may be stored for on demand processing and review. The total energy and position information may be used together or individually to limit whether the information is accepted for later processing or storage. The combination of position and energy information represents a single event.
One method for starting the storage of acquisition data for gamma cameras can involve a manual interaction and initiation of the starting point for the storage of acquired data. This manual start may be further qualified by incorporating a count down timer function or event rate detection. A manual start may include a second person to initiate the acquisition on command, sometimes referred to as “shout and start”. Another derivative of the manual start can include the use of a remote mechanical switch, for example a foot pedal switch, which can be actuated by an operator to initiate the acquisition of data.
A time invariant alternative to manual initiation of data acquisition may include monitoring for a specified event rate level to initiate acquisition. However, when the sensitivity of this method is set sufficiently low to begin the capturing of data at the first appearance of the activity, there may be a tendency to falsely trigger due to activity entering the field of view independently of the acquisition of interest. An event rate level starting system may suffer from false starts due to normal changes in the environment resulting in activity increases not associated with the acquisition interval of interest. Also, when set to a level to avoid inadvertent triggering, substantial pre-start condition data may not be available for analysis.
During the transit of the bolus, it may be desirable to start acquiring data at a time that provides complete storage of the time interval of interest while minimizing the storage of unnecessary and uninteresting time intervals. The use of manual methods for beginning the acquisition of data may increase an operator's workload or require the introduction of, and communication with, a second operator. The use of time invariant automatic methods for beginning the acquisition of the data may not provide a consistent and repeatable method for storage or take in to account the variable nature of the setup and initiation of the acquisition.
The quality and repeatability of acquisitions of the prior art is wanting, however. Operator variability and the need for multiple operators is a major shortcoming. It would be desirable to provide automatic acquisition interval identification and storage in an attempt to eliminate problems associated with prior manual, count down timer, and simple event level starting systems, or a combination of those systems.